An Internet Protocol (IP) address typically comprises a series of domains arranged in a hierarchical series. Specifically, an IP address may begin with a broad IP domain, which is followed by a plurality of more specific IP domains within each preceding domain. When the devices associated with IP addresses (IP devices) are relatively stationary, it is possible to determine which networks the IP device is associated with based on the domains in the IP addresses. Such a hierarchical structure of the IP address aids in routing messages, packets, and other data to the IP device. If the IP device moves to another network having a different IP domain, then the IP device can be issued a new IP address consistent with that domain, using a protocol such as dynamic host configuration protocol (DHCP). However, when an IP device is mobile (mobile station (MS)), the issuance of a new IP address to the MS every time the MS changes networks is an unattractive solution.
One solution to the above problem is to issue the MS a relatively permanent IP address, such as one associated with the MS's home network, and use the mobile IP (MIP) protocol to tunnel between the MS's home network and the foreign network to which the MS is connected. The MIP protocol ensures that a moving MS can continue to receive packets while maintaining an IP address assigned in a different network. Unfortunately, many MSs do not support MIP. In order to make those MSs without MIP capability have the same mobility performance as those with MIP capability, WiMAX has designed a Proxy MIP (PMIP) protocol. The PMIP protocol includes a network entity called a PMIP client that has MIP capability and conducts MIP operations on behalf of the MS. Since the MSs use DHCP to obtain IP addresses, the PMIP protocol includes a network entity called a DHCP proxy that provides the behavior expected by the MS from a DHCP server.